Bruce Lee's biographer, Matthew Polly, called him a "kinetic genius" when it came to martial arts (per CNN). He had a knack for picking up physical combat skills and could very quickly become adept at a new style. What he couldn't learn quickly, at least in his youth, were the basic lessons taught at school. A hyperactive and restless boy, Lee couldn't stand sitting for long hours in the classroom, and despite loving reading in his spare time, could not or would not engage with his textbooks. One of the teachers at his Catholic school (via Polly's "Bruce Lee: A Life") remembered him as "a proverbial devil in the holy water soup," and he regularly failed his classes.
Lee's parents tried to help him by hiring a private tutor, but Lee simply skipped his lessons. Fighting held more of an appeal for him than school, and street gangs were a ready-and-waiting outlet. Lee led his own gang, which was more mischievous than dangerous. But their antics still worried his parents, and his father threatened, and sometimes did, take away performing and theater from Lee as a punishment. His antics continued into college, and he was eventually expelled.
Ironically, martial arts proved a useful outlet for a young Lee's energy, as his teachers and parents all found. One teacher, Brother Edward Muss, introduced him to boxing, and Lee would later blend boxing with the wing chun form of kung fu in a match with an English opponent, and to good effect.
